Make a Page Hidden/Visible

In edit mode, on the Properties tab, checking the Visible in Navigation box makes a page visible in the site navigation.

Conversely, unchecking the Visible in Navigation box drops a page into the Hidden Pages section and makes it NOT appear in the site navigation (though it IS still on the web server and can be linked to and visited on the live site). By default, hidden pages CAN be found in search. See the page Hide a Page from Search for a reminder of how to stop a page from showing up in search.